OBJECTIVE: to explore the relationship between bacterial cystitis and bladder pressures. There is evidence in the young child that cystitis is associated with bladder dysynnergia, the detrusor muscle working against a spastic external sphincter, and that high pressures during bladder filling, and at and after voiding, occur. If so, these may be severe enough to produce vesico-ureteral reflux of sufficient pressure to cause intrarenal reflux and acute focal nephritis which later gives rise to large scars. (Reflux nephropathy.) This sequence has been produced in 1 pilot study (pig). After basic bladder pressures have been taken, cystitis will be established in 10 pigs with a known organism and the ensuing bladder pressures monitored at short and, later, more prolonged intervals. Upper tract damage will be assessed by urography. If scarring occurs a proportion of the animals will be sacrificed to define the pathology present and the remainder kept to see how soon hypertension ensures. It is anticipated raised bladder pressure will ensue within days of establishing infection.